1. Field of the Invention
The present invention relates to a power supply circuit provided with a capacitor for accommodating the voltage regulation (voltage variation) of a battery.
2. Description of the Related Art
In recent years, power supply circuits having a capacitor which is connected (in parallel) to a battery to suppress the voltage regulations of a battery have been proposed. Since a capacitor whose ESR (equivalent series resistance) is low, and whose accumulate capacitance is large, is suitable for such power supply circuits, an electric double layer capacitor is mainly used.
However, in the case where the electric double layer capacitor is connected in parallel to a secondary (or rechargeable) battery (e.g., a rechargeable lithium-ion battery) provided with an overcurrent protective circuit, a large (heavy) electric current is drawn from the battery when the electric double layer capacitor is charged, which may actuate the overcurrent protective circuit to interrupt the output current of the battery to the electric double layer capacitor. Accordingly, if the overcurrent protective circuit is actuated to interrupt the output current of the battery to the electric double layer capacitor, since the operator cannot determine whether the overcurrent protective circuit has been actuated, in most cases an operator mistakenly determines that the battery is empty (xe2x80x98flatxe2x80x99) even though the battery is not, or mistakenly determines that the electronic device to which the power supply circuit is connected has broken down. If the operator mistakenly determines that the battery is empty, the battery ends up being replaced by a new one even though the battery still has enough power, and the remaining power of the battery is wasted.
An object of the present invention is to provide a power supply circuit provided with a capacitor for accommodating the voltage regulations(voltage variations) of a battery, wherein the overcurrent protective circuit of the battery can be prevented from being actuated while the capacitor is being charged.
To achieve the object mentioned above, according to an aspect of the present invention, a power supply circuit is provided, which is connected to a battery having an overcurrent protective device, the power supply circuit including a capacitor which is connected in parallel to the battery to be charged by the battery, and a restricting device which restricts an output current of the battery so that the output current of the battery is not interrupted by the overcurrent protective device while the capacitor is being charged with the battery.
Preferably, the power supply circuit further includes a voltage detector which detects a terminal voltage across the capacitor, wherein the restricting device restricts the output current of the battery in accordance with the terminal voltage detected by the voltage detector.
Preferably, the restricting device restricts the output current of the battery in accordance with the terminal voltage detected by the voltage detector so that a the output current of the battery becomes maximum within a range in which the overcurrent protective device is not actuated to interrupt the output current of the battery to the power supply circuit.
In an embodiment, the restricting device includes a variable resistor via which the battery is connected to the capacitor, and a controller which controls the output current of the battery by varying a resistance value of the variable resistor in accordance with the terminal voltage detected by the voltage detector.
In an embodiment, the restricting device includes a plurality of resistors connected in parallel via which the battery is connected to the capacitor; a plurality of switches with which each of the plurality of resistors can be connected to and disconnected from one of the battery and the capacitor; and a controller which controls the plurality of switches independently of one another in accordance with the terminal voltage detected by the voltage detector.
In an embodiment, the restricting device includes a plurality of field effect transistors connected in parallel via which the battery is connected to the capacitor, and a controller which controls an ON/OFF state of each of the plurality of field effect transistors in accordance with the terminal voltage detected by the voltage detector.
In an embodiment, the restricting device includes a field effect transistor via which the battery is connected to the capacitor; and a controller which controls the output current of the battery by controlling a voltage across a gate and a source of the field effect transistor in accordance with the terminal voltage detected by the voltage detector.
In an embodiment, the restricting device includes a transistor, wherein a collector of the transistor is connected to a gate of the field effect transistor while an emitter of the transistor is connected to ground, and the controller controls the voltage across the gate and a source of the field effect transistor by controlling a base voltage of the transistor.
In an embodiment, the power supply circuit further includes a plurality of resistors and a plurality of switches which are turned ON and OFF so that a base of the transistor is connected to and disconnected from the ground via the plurality of resistors, respectively. The controller controls the base voltage of the transistor by changing ON/OFF states of the plurality of switches.
According to an aspect of the present invention, a power supply circuit is provided, which is connected to a battery having an overcurrent protective device, the power supply circuit including a capacitor, a first switch provided in a primary path for connecting the battery with the capacitor, a second switch provided in an alternative path for connecting the battery with the capacitor, a voltage detector which detects a terminal voltage across the capacitor, and a charge control device which controls a switching operation of the first switch to intermittently charge the capacitor with the battery via the primary path in the case where the terminal voltage Vc across the capacitor is smaller than a predetermined threshold value. The charge control device switches the primary path to the alternative path to continuously charge the capacitor with the battery via the alternative path in the case where the terminal voltage across the capacitor exceeds the predetermined threshold value.
In an embodiment, a duration of an ON state of the first switch in an intermittent charging operation, in which the capacitor is charged intermittently, is shorter than a time necessary for the overcurrent protective device to detect an overcurrent of the battery.
In an embodiment, a duration of an ON state of the to first switch in an intermittent charging operation, in which the capacitor is charged intermittently, is shorter than a duration from the moment the battery is connected to the capacitor to the moment an output current of the battery exceeds an overcurrent detection value of the overcurrent protective device.
According to an aspect of the present invention, a power supply circuit is provided, which is connected to a battery having an overcurrent protective device, the power supply circuit including a capacitor, an adjusting condenser connected in parallel with the battery, the adjusting condenser having a capacitance so that when the capacitor is charged with the battery, the overcurrent protective device is not actuated to interrupt an output current of the battery to the power supply circuit; a switching element with which the adjusting condenser can be connected to and disconnected from the capacitor; and a charge control device which controls a switching operation of the switching element to intermittently charge the capacitor with power output from the battery and the adjusting condenser.
In an embodiment, the capacitor is charged with power output from the battery and the adjusting condenser when the switching element is ON, and the capacitor is charged with power output only from the battery when the switching element is OFF.
In an embodiment, the power supply circuit further includes a voltage detector which detects a terminal voltage across the capacitor. In the case where the terminal voltage becomes one of equal to and greater than a predetermined voltage, the charge control device stops the switching operation of the switching element, and connects the battery and the adjusting condenser to the capacitor via the switching element.
According to an aspect of the present invention, a power supply circuit is provided, which is connected to a battery having an overcurrent protective device, the power supply circuit including a first capacitor which can be connected in parallel to the battery; a second capacitor which can be connected in parallel to the first capacitor; and a charge control device which controls a charging operation for charging the first capacitor and a charging operation for charging the second capacitors. The charge control device repeats a main charging operation and a relay charging operation alternately. The first capacitor is connected to the battery with the first capacitor being disconnected from the second capacitor, in order to charge the first capacitor with the battery in the main charging operation. The first capacitor is connected to the second capacitor with the first capacitor being disconnected from the battery, in order to charge the second capacitor with power output from the first capacitor.
In an embodiment, the second capacitor includes a plurality of capacitors connected in parallel.
In an embodiment, the power supply circuit further includes a switching device provided between the battery and the first capacitor. In the main charging operation, the charge control device controls a switching operation of the switching device to intermittently charge the first capacitor.
In an embodiment, the charge control device repeats the main charging operation and the relay charging operation alternately until a terminal voltage across the first capacitor becomes equal to or greater than a predetermined reference voltage at which an output current of the battery can be prevented from being interrupted by the overcurrent protective device.
In an embodiment, the charge control device performs the main charging operation when the terminal voltage across the first capacitor is smaller than a predetermined threshold voltage, and performs the relay charging operation when the terminal voltage across the first capacitor is one of equal to and greater than the predetermined threshold voltage.
In an embodiment, the charge control device supplies power output from the battery and the first capacitor to a load while performing the main charging operation, and the charge control device supplies power output only from the battery to the load while performing the relay charging operation.
In the case where the terminal voltage across the first capacitor is equal to or greater than a predetermined reference voltage at which an output current of the battery can be prevented from being interrupted by the overcurrent protective device, in a state where the second capacitor is connected in parallel to the first capacitor, the charge control device connects the battery to the first or second capacitor to supply power output from the battery and the respective first or second capacitor to the load.
Preferably, the capacitor is an electric double layer capacitor.
Preferably, the battery is a rechargeable lithium-ion battery.
In an embodiment, the restricting device includes a microcomputer including a voltage detector, a memory and a comparator.
In an embodiment, the variable resistor includes a plurality of resistors and a corresponding group of switches for switching ON/OFF states of the plurality of resistors.
In an embodiment, the controller controls the resistance value of the variable resistor from a high resistance value to a low resistance value as the terminal voltage detected by the voltage detector increases.
The present disclosure relates to subject matter contained in Japanese Patent Applications No.2000-109125 (filed on Apr. 11, 2000), No.2000-113509 (filed on Apr. 14, 2000), No.2000-113710 (filed on Apr. 14, 2000) and No.2000-143002 (filed on May 16, 2000) which are expressly incorporated herein by reference in their entireties.